Explanation:

A context-free grammar (CFG) is a formal grammar used to describe the syntax of a programming language or other formal languages. It consists of a set of production rules that specify how symbols can be combined to form strings.

Terminal Symbol:
Terminal symbols are the basic building blocks of a language. They are the smallest units of a language that cannot be further divided. Terminal symbols represent the actual words or symbols that appear in the language. For example, in the context of a programming language, terminal symbols can represent keywords, operators, identifiers, literals, etc.

Non-terminal Symbol:
Non-terminal symbols are placeholders that represent groups of terminal symbols. They are used to define the structure of the language. Non-terminal symbols do not appear directly in the final language, but they are used in the production rules to specify how terminal symbols can be combined. For example, non-terminal symbols can represent expressions, statements, functions, etc.

Start Symbol:
The start symbol is a special non-terminal symbol that represents the beginning of the language. It is used to indicate where the derivation of a string should start. The start symbol is typically the left-hand side of the first production rule.

End Symbol:
Unlike the other three symbols, there is no concept of an "end symbol" in the context of a CFG. A CFG describes the structure of a language, but it does not specify how a string ends. The end of a string is typically determined by the specific language or parser that is used to process the string.

Therefore, the correct answer is option 'D' (End Symbol) as it does not belong to the context-free grammar.